Use the following to answer questions:
The diagram below shows the steps used in microarray analysis to detect differences in expression between tumor tissue and normal tissue. 
-At which step does reverse transcription occur?
Definitions:
Interaction
A statistical term describing a situation in which the effect of one explanatory variable on the response variable depends on the level of another explanatory variable.
Main Effects
In statistics and experimental design, the direct impact of an independent variable on a dependent variable, disregarding interactions with other variables.
Profile Plot
A graphical representation that shows trends and interactions in data across different variables, typically used in multivariate analysis.
Main Effect
In the context of experimental design, it refers to the primary influence of an independent variable on a dependent variable.
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